1. Field of the Invention
The present invention relates to an encoder having a function of adjusting a threshold value of a comparator used in the encoder and a method for controlling the encoder.
2. Description of Related Art
Encoders are used for detecting movement directions, movement amounts, or angles of rotating or moving objects. In the encoders, it is sometimes necessary to adjust the signals from the encoders in order to realize position detection with high accuracy. For example, a threshold value to be used for a comparison with an analog signal of the encoder is adjusted before shipping the product of the encoder. However, this increases tact time, and when the signal level varies with a lapse of time after shipment, it is difficult to readjust the threshold value. In other words, the analog signal adjustment before the shipment, by itself, cannot deal with a reduction in the amplitude of the analog signal outputted from a detection unit, due to aging deterioration of the encoder or the occurrence of an offset.
A comparator (comparator circuit) and an encoder that can convert a sinusoidal input signal into a rectangular wave with high accuracy without being affected by waviness of the input signal from a detection unit are known (for example, Japanese Unexamined Patent Publication (Kokai) No. 2010-019676). The conventional comparator includes an input unit to which the substantially sinusoidal input signal is inputted from the detector, a peak value calculation unit for calculating the peak value of the substantially sinusoidal input signal inputted to the input unit, a bottom value calculation unit for calculating the bottom value of the substantially sinusoidal input signal inputted to the input unit, a threshold value calculation unit for calculating a threshold value in a range between the peak value calculated by the peak value calculation unit and the bottom value calculated by the bottom value calculation unit, and a threshold value setting unit for setting the threshold value to convert the substantially sinusoidal input signal into a rectangular wave signal.